The present invention relates to a safety device and, more particularly, to a safety harness to be worn by a person to protect that person from injury in case of a fall.
Safety harnesses are commonly used as part of a fall protection system for persons subjected to the potential of a fall from a height. In the workplace, full-body safety harnesses are generally used. Such harnesses, which typically include shoulder straps, can be designed in many alternative manners. See, for example, U.S. Pat. Nos. 5,531,292, 5,329,884, and 5,203,829.
Currently available full-body safety harnesses are generally manufactured from flexible, but relatively inelastic, woven materials such as nylon and polyester. Such materials are generally capable of an elastic extension of approximately 1% or less under a tensile load of approximately 10 pounds. Indeed, even at a tensile load of approximately 100 pounds, such materials generally exhibit an elastic extension of approximately 2.5% or less. Although the strength of such materials is suitable for fall protection, harnesses fabricated from such materials impair movement of a worker while in the harness. This impairment of movement often results in discomfort, reduced effectiveness and quick fatigue of the worker. The limited range of motion, discomfort and fatigue associated with current safety harnesses can result in safety lapses by the worker. Various attempts at redesigning safety harnesses to provide greater comfort and range of motion have met with very limited success.
It is, therefore, very desirable to develop safety harnesses that do not suffer from such drawbacks.
In general, the present invention provides a safety harness to be worn by a person. The safety harness comprises a strap portion for extending over a portion of the person""s body to retain the person within the safety harness. At least a portion or section of the strap portion exhibits an elastic extension of at least 3% under a tensile load of approximately 20 pounds, and, more preferably, at a tensile load of approximately 10 pounds, thereby facilitating movement of the person within the safety harness. Preferably, at least a portion of the strap portion is adapted to exhibit an elastic extension in the range of approximately 3% to approximately 20% under a tensile load of approximately 20 pounds, and, more preferably, under a tensile load of approximately 10 pounds. More preferably, the elastic extension is in the range of approximately 3% to approximately 15% under such tensile loading. Most preferably, the elastic extension is in the range of approximately 7% to approximately 11% under such tensile loading. Preferably, substantially the entire strap portion or the entire strap portion is fabricated from a material exhibiting an elastic extension within the above ranges.
As used herein, percent elastic extension under a particular tensile loading is calculated using the following formula:
(Length(extended)xe2x88x92Length(initial))/Length(initial)*100%
Over the range of elastic extension, the elastic materials used in the strap portions of the present invention preferably return to substantially their original (non-extended) length from an extension within the range of elastic extension when a tensile load is removed.
As used herein, the term xe2x80x9cnon-elasticxe2x80x9d refers generally to materials having an elastic extension of less than approximately 3% under a tensile load of approximately 10 pounds.
The present inventors have discovered that use of material(s) capable of elastic extension of at least approximately 3% at a tensile load of approximately 10 to 20 pounds in one or more of the support strap-portions of a safety harness greatly reduces, if not eliminates, the problems of limited motion and associated fatigue experienced with currently available safety harnesses. Additionally, incorporation of such elastic materials into one or more support strap portions of the present invention assists in creating a snug fit without restricting movement. Unlike currently available safety harnesses, there is substantially no need for frequent readjustment of the fit of the safety harnesses of the present invention. Moreover, the snug fit of the safety harnesses of the present invention substantially prevents sections of the strap portion from hanging away from the user""s body, thereby reducing the risk that such hanging strap portion may snag some object or machinery in the work area.
In general, an extension (whether elastic or not) of a strap portion of greater than approximately 20% is undesirable, because of the increased risk that the user may come out of the harness. Such relatively large extensions are preferably avoided under normal working conditions and in fall arresting situations when tensile loads on support straps can be relatively large. Preferably, therefore, the elastic support straps of the present invention do not experience an elastic extension of greater than 20% under such conditions. The support strap(s) of the present invention preferably do not experience extension of greater than approximately 20% even under tensile loads up to approximately 100 pounds and, more preferably, at tensile load up to approximately 1,000 pounds.
In addition to exhibiting the above elastic characteristics, the elastic strap portion(s) of the present invention must be capable of withstanding the tensile forces experienced in common use and in arresting falls. Preferably, the elastic strap portion(s) of the present invention have a minimum ultimate tensile load of approximately 5,000 pounds. An ultimate tensile load of 5,000 pounds is a common industry standard.
In one embodiment, the present invention provides a full-body safety harness comprising an upper torso portion having a shoulder strap portion for extending over a respective shoulder of the person. As described above, at least a section of the shoulder strap exhibits an elastic extension of at least 3% at a tensile load of approximately 20 pound and, more preferably, at a tensile load of approximately 10 pounds. Preferably, at least a section of the shoulder strap portion is adapted to have an elastic extension in the range of approximately 3 to approximately 20% under a tensile load of approximately 20 pounds and, more preferably, under a tensile load of approximately 10 pounds.